Krauzlis Lab Projects

The role of the superior colliculus in target selection

The superior colliculus (SC) is a midbrain structure that is important for orienting movements in a variety of species. In primates, the deeper layers of the SC contain neurons that have been extensively studied for their role in the control of saccades. However, several years ago, we found that neurons in the rostral SC (the portion representing the central visual field) are strongly modulated during pursuit (Krauzlis et al., 1997, 2000), and that altering activity in the SC affects pursuit as well as saccades (Basso et al., 2000). We speculated that the SC processes a shared signal that could coordinate the two eye movement systems.

This idea is at odds with textbook descriptions of eye movements: the SC is a central component of the pathways for saccades, but has never been considered part of the pursuit system. A major focus of our research has been to identify the function of this shared signal. Our most significant result is the demonstration that the SC is involved in the process of target selection, distinct from its traditional role in the motor preparation of saccades.

We have identified the following properties of pursuit-related activity in the SC:

It is not simply a visual response, because it persists in the absence of a visual target (Krauzlis, 2001).
It does not convey motion signals for pursuit, because it is not directionally selective (Krauzlis, 2004).
On the other hand, we showed that this activity predicts the choices made by pursuit. During a visual search task, many SC neurons exhibit a preference for a “target” stimulus over an irrelevant “distractor” stimulus, and this preference emerges over the course of ~100 ms prior to the initiation of pursuit and saccades (Krauzlis and Dill, 2002).
By interpreting the preference for target stimuli as a “decision signal”, we demonstrated that SC activity could account for the target choices made by pursuit and saccades (Krauzlis and Dill, 2002).
We found that pursuit uses a less stringent decision criterion than saccades (Krauzlis and Dill, 2002), perhaps because errant saccades are more costly in their disruption of vision than mistakes by pursuit, corroborating our previous suggestion that pursuit and saccades employ different tradeoffs between speed and accuracy (Krauzlis et al., 1999).
We have directly tested these ideas by altering activity in the SC with weak microstimulation (i.e., too weak to evoke movements directly) as monkeys identified a target in the presence of a distractor and reported their answers with either pursuit or saccades. Microstimulation increased the number of correct responses when the target location matched the stimulation site and decreased correct responses when the target location did not match (Carello and Krauzlis, 2004).
The microstimulation results for pursuit were especially revealing. Because the target for pursuit initially appeared at a location opposite to its direction of motion, we could distinguish whether microstimulation changed the motor command (i.e., which direction to move) or the goal of the movement (i.e., which stimulus to follow). We discovered that the effect of SC microstimulation was associated with the location of the stimulus, not the direction of the eye movement, indicating that tickling activity in the SC with microstimulation affected target selection by altering the movement goal (Carello and Krauzlis, 2004).

These results argue for a new interpretation of SC function – it participates in the process of target selection by representing the movement goal, but does not dictate the motor details of how that goal will be achieved. This may reflect a general property of sensory-motor control: basing movement decisions on a common goal ensures that different motor outputs are coordinated, whereas applying different decision criteria allows flexibility in the programming of each type of movement.
Our microstimulation results imply that the locus of activity in the SC may not directly determine the movement endpoint, but can act indirectly, like a pointer, to identify the source of information that should guide the movement. This function of the SC would presumably involve feedback projections to regions of cerebral cortex and argues that the SC may be part of a circuit for controlling the allocation of visual attention.

References

Basso MA, Krauzlis RJ, Wurtz RH. Activation and inactivation of rostral superior colliculus neurons during smooth-pursuit eye movements in monkeys. J Neurophysiol., 84:892-908, 2000. PDF

Carello, C.D. and Krauzlis, R.J., Manipulating intent: evidence for a causal role of the superior
colliculus in target selection, Neuron, 43: 575-583, 2004. PDF

Krauzlis R, Dill N. Neural correlates of target choice for pursuit and saccades in the primate superior colliculus. Neuron, 35:355-363, 2002. PDF

Krauzlis RJ. Extraretinal inputs to neurons in the rostral superior colliculus of the monkey during smooth-pursuit eye movements. J Neurophysiol., 86:2629-2633, 2001. PDF

Krauzlis, R.J., Activity of the rostral superior colliculus during passive and active viewing of motion, J Neurophysiol., 92:949-958, 2004. PDF

Krauzlis R.J., Basso M.A., and Wurtz R.H., Shared motor error for multiple eye movements. Science, 276:1693-1695, 1997. PDF

Krauzlis R.J., Basso M.A., and Wurtz R.H., Discharge properties of neurons in the rostral superior colliculus of the monkey during smooth-pursuit eye movements. J Neurophysiol., 84:876-891, 2000. PDF

Krauzlis R.L., Zivotofsky A.Z., and Miles F.A., Target selection for pursuit and saccadic eye movements in humans. J Cogn Neurosci., 11:641-649, 1999. PDF

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	The role of the superior colliculus in target selection The superior colliculus (SC) is a midbrain structure that is important for orienting movements in a variety of species. In primates, the deeper layers of the SC contain neurons that have been extensively studied for their role in the control of saccades. However, several years ago, we found that neurons in the rostral SC (the portion representing the central visual field) are strongly modulated during pursuit (Krauzlis et al., 1997, 2000), and that altering activity in the SC affects pursuit as well as saccades (Basso et al., 2000). We speculated that the SC processes a shared signal that could coordinate the two eye movement systems. This idea is at odds with textbook descriptions of eye movements: the SC is a central component of the pathways for saccades, but has never been considered part of the pursuit system. A major focus of our research has been to identify the function of this shared signal. Our most significant result is the demonstration that the SC is involved in the process of target selection, distinct from its traditional role in the motor preparation of saccades. We have identified the following properties of pursuit-related activity in the SC: It is not simply a visual response, because it persists in the absence of a visual target (Krauzlis, 2001). It does not convey motion signals for pursuit, because it is not directionally selective (Krauzlis, 2004). On the other hand, we showed that this activity predicts the choices made by pursuit. During a visual search task, many SC neurons exhibit a preference for a “target” stimulus over an irrelevant “distractor” stimulus, and this preference emerges over the course of ~100 ms prior to the initiation of pursuit and saccades (Krauzlis and Dill, 2002). By interpreting the preference for target stimuli as a “decision signal”, we demonstrated that SC activity could account for the target choices made by pursuit and saccades (Krauzlis and Dill, 2002). We found that pursuit uses a less stringent decision criterion than saccades (Krauzlis and Dill, 2002), perhaps because errant saccades are more costly in their disruption of vision than mistakes by pursuit, corroborating our previous suggestion that pursuit and saccades employ different tradeoffs between speed and accuracy (Krauzlis et al., 1999). We have directly tested these ideas by altering activity in the SC with weak microstimulation (i.e., too weak to evoke movements directly) as monkeys identified a target in the presence of a distractor and reported their answers with either pursuit or saccades. Microstimulation increased the number of correct responses when the target location matched the stimulation site and decreased correct responses when the target location did not match (Carello and Krauzlis, 2004). The microstimulation results for pursuit were especially revealing. Because the target for pursuit initially appeared at a location opposite to its direction of motion, we could distinguish whether microstimulation changed the motor command (i.e., which direction to move) or the goal of the movement (i.e., which stimulus to follow). We discovered that the effect of SC microstimulation was associated with the location of the stimulus, not the direction of the eye movement, indicating that tickling activity in the SC with microstimulation affected target selection by altering the movement goal (Carello and Krauzlis, 2004). These results argue for a new interpretation of SC function – it participates in the process of target selection by representing the movement goal, but does not dictate the motor details of how that goal will be achieved. This may reflect a general property of sensory-motor control: basing movement decisions on a common goal ensures that different motor outputs are coordinated, whereas applying different decision criteria allows flexibility in the programming of each type of movement. Our microstimulation results imply that the locus of activity in the SC may not directly determine the movement endpoint, but can act indirectly, like a pointer, to identify the source of information that should guide the movement. This function of the SC would presumably involve feedback projections to regions of cerebral cortex and argues that the SC may be part of a circuit for controlling the allocation of visual attention. References Basso MA, Krauzlis RJ, Wurtz RH. Activation and inactivation of rostral superior colliculus neurons during smooth-pursuit eye movements in monkeys. J Neurophysiol., 84:892-908, 2000. PDF Carello, C.D. and Krauzlis, R.J., Manipulating intent: evidence for a causal role of the superior colliculus in target selection, Neuron, 43: 575-583, 2004. PDF Krauzlis R, Dill N. Neural correlates of target choice for pursuit and saccades in the primate superior colliculus. Neuron, 35:355-363, 2002. PDF Krauzlis RJ. Extraretinal inputs to neurons in the rostral superior colliculus of the monkey during smooth-pursuit eye movements. J Neurophysiol., 86:2629-2633, 2001. PDF Krauzlis, R.J., Activity of the rostral superior colliculus during passive and active viewing of motion, J Neurophysiol., 92:949-958, 2004. PDF Krauzlis R.J., Basso M.A., and Wurtz R.H., Shared motor error for multiple eye movements. Science, 276:1693-1695, 1997. PDF Krauzlis R.J., Basso M.A., and Wurtz R.H., Discharge properties of neurons in the rostral superior colliculus of the monkey during smooth-pursuit eye movements. J Neurophysiol., 84:876-891, 2000. PDF Krauzlis R.L., Zivotofsky A.Z., and Miles F.A., Target selection for pursuit and saccadic eye movements in humans. J Cogn Neurosci., 11:641-649, 1999. PDF
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